1. Field of the Invention
This invention relates to an optical recording and reproducing apparatus, such as a magneto-optical recording and reproducing apparatus used, for example, as an external memory device for an electronic computer or a device for recording and reproducing audio and visual signals and other information.
2. Prior Art
With the recent development of electronic computers and high-speed mass information transfer means, there has been a demand for a non-volatile memory device which is inexpensive, having a high density and a large capacity, and which is capable of high-speed transfer. For this reason, in many cases, magnetic disk devices have been used. However, such a magnetic disk device has problems such as a low recording density, a high cost per unit information, and limited environments of use of the magnetic disk device. Optical recording has now been spotlighted as a technology for overcoming such problems.
Generally, in an optical recording and re-producing apparatus, a movable optical system including an objective lens is moved along a guide shaft extending radially of a recording medium so as to achieve access to data. Generally, to achieve a cost reduction, guide means for supporting the movable optical system in a manner to allow the movement of this optical system in a direction parallel to the guide shaft is constituted by a cylindrical sliding member mounted around the guide shaft. The movable optical system is fixedly secured to the outer peripheral surface of the sliding member. Since the sliding member is slidable relative to the guide shaft, the movable optical system is movable along the length of the guide shaft. However, this sliding support means allows unnecessary rotation of the movable optical system about the guide shaft, in addition to a translational motion of the movable optical system along the guide shaft. Therefore, it is necessary to provide means for limiting such rotation. Such rotation limiting means comprises an auxiliary guide shaft extending parallel to the guide shaft, and a rolling member mounted on the movable optical system and held in rolling contact with the auxiliary guide shaft. Thus, in the support means of the general type used in the conventional optical recording and reproducing apparatus, the guide shaft supports the movable optical system in a manner to allow a sliding movement of the same, and the auxiliary guide shafts support the movable optical system through the rolling contact.
That is, a guide means for a movable optical system in an optical recording and reproducing apparatus has in general a guide shaft for slidably supporting the movable optical system and an auxiliary guide shaft for supporting the same in a rolling contact manner.
Generally, with respect to the thrust applied at the time of the access operation, a thrust vector passes through the center of gravity of the movable optical system. For example, if drive coils are provided respectively on the opposite sides of the movable optical system and outside of the guide shaft, the resultant thrust vector due to the drive coils can be designed to pass through the center of gravity of the movable optical system. This arrangement can present the generation of a moment due to the inertia force acting on the movable optical system during the access acceleration.
However, with such conventional arrangement, the following problems are encountered. Namely, during the operation, the sliding member is subjected to a friction force, and when the line of action of the friction force is not in alignment with the line of action of the thrust, a moment is produced. This moment is received by the sliding member, and a reaction moment is produced. The resulting reaction force also develops in the sliding member. In other words, during the movement of the movable optical system, the sliding member is subjected to a large friction force, so that acceleration characteristics of the movable optical system are greatly deteriorated. Further, the reliability of the sliding member which is likely to wear is adversely affected greatly.
Further, various forces are produced due to disturbances, and therefore vibrations are produced because of a small clearance between the sliding member and the guide shaft, so that the controllability of the movable optical system is adversely affected greatly. Particularly when disturbance develops in a direction perpendicular to a plane including the axes of the guide shaft and the auxiliary guide shaft, the inertia force appearing at the center of gravity of the movable optical system produces a moment about the sliding member. The reaction moment against this moment acts as a reaction force on the rolling member (rotation limiting member) on the auxiliary guide shaft. When acceleration disturbance of a large magnitude, such as an impact, develops, this reaction force may exceed the withstanding strength of the rolling member, which lowers the reliability. In other words, the guide structure for the movable optical system of the above conventional optical recording and reproducing apparatus can be quite easily affected by the disturbances.